The present invention provides for methods for forming a low-k dielectric film on semiconductors wafers or integrated circuits using an asymmetric organocyclosiloxane compound as a CVD extra low-k dielectric precursor.
The increase in semiconductor design integration by feature size reduction has resulted in increased levels of interconnect and increased utilization of dielectric low-k thin films. The dielectric film is used as insulation around metal lines of a device, and it contributes to the RC time constant that controls the device speed. As the semiconductor industry has strived to reduce resistance (R) by the use of copper metallization, the push to the use of low-k dielectrics is to reduce capacitance (C). Reducing capacitance by lowering the dielectric constant k to the inter and intra level dielectric (ILD) film can improve device performance by reducing the RC time delay, decreasing the cross talk between adjacent metal lines and lowering the power dissipation.
Traditionally, the material of choice for the ILD is silicon dioxide (SiO2) which can be prepared using silane, disilane or siloxane precursors in an oxidizing environment. The most popular deposition techniques for depositing ILD are chemical vapor deposition (CVD), low temperature plasma-enhanced CVD (PECVD), or high-density plasma CVD (HDPCVD). However, the dielectric constant of the deposited SiO2 is relatively high at 4.0.
As the semiconductor industry moves to smaller width metal lines, low-k materials must have smaller dielectric constants. Industry publications have indicated that low-k materials with k values from 2.7 to 3.5 would be needed for 150 and 130 nm technology modes. When the industry moves to 100 nm technology and dimensions below that in the future, extra low-k (ELK) materials having a k value from 2.2 to 2.6 and ultra low-k (ULK) materials with a k value less than 2.2 will be necessary.
The semiconductor industry has developed several low-k materials to replace silicon dioxide that are inorganic, organic or hybrid materials. These materials can be deposited by either chemical vapor deposition (CVD) or spin-on deposition (SOD) methods. The CVD technique utilizes existing vacuum tools for depositing SiO2 that include lower temperature plasma enhanced CVD (PECVD) and high density plasma CVD (HDP-CVD). The SOD method uses spin coaters that have shown better extendibility to ELK or ULK by introducing pores in nanometer sizes. Newer materials such as fluorossilicate glass (FSG), carbon or carbon fluorine based films and carbon-doped SiO2 utilize CVD techniques. Materials such as polyimide, hydrogen silsesquioxane (HSQ) and polyarylene ethers can be deposited using SOD techniques.
As such, a number of technologies to provide lower dielectric constant CVD materials have been demonstrated in the 3.5 to 2.6 range. However, there are far fewer alternatives for k values at or below 2.5 for CVD materials in ELK/ULK applications. The present invention provides for new materials for use as extra low dielectric CVD precursors in extra low-k CVD materials for the semiconductor industry.
Given the desires of the semiconductor industry for lower k value materials, new low-k CVD materials are being sought. The present invention provides a novel class of compounds useful for forming a film on a semiconductor or integrated circuit by acting as a precursor for the film formed when the compound is applied.
Asymmetric organocyclosiloxane compounds are used as precursors for forming a low-k dielectric film on the surface of semiconductor wafers and integrated circuits. The resultant dielectric film formed will be an organosilicon polymer film on the surface of the device, which will have low-k dielectric properties.
The asymmetric organocyclosiloxane compounds are those having the formula (xe2x80x94SiOxe2x80x94)nR(2n-m)Rxe2x80x2m where (xe2x80x94SiOxe2x80x94) represents a cyclic siloxane ring; n is the number of (xe2x80x94SiOxe2x80x94) units in the ring, which is 3 or higher; R is an acyclic alkyl-containing hydrocarbon from C1 to C7; Rxe2x80x2 is H, a vinyl group, or a cyclohexyl group, and m is 1 or higher with the stipulation that the molecule remains asymmetric. In some cases, the two groups, R and Rxe2x80x2, are linked together to form a cyclic alkyl group.
The asymmetric organocyclosiloxane compounds are precursors to the film formed and will react with the surface of the semiconductor wafers or integrated circuits to form the extra low-k dielectric film having a dielectric constant less than 2.5.
The present invention provides for a method of fabricating a dielectric film on a semiconductor or integrated circuit wherein the dielectric film will be a low-k film comprising applying to the surface of the semiconductor or integrated circuit an asymmetric organocyclosiloxane compound.
The asymmetric organocyclosiloxane compound has the general formula:
(xe2x80x94SiOxe2x80x94)nR(2n-m)Rxe2x80x2m
wherein (xe2x80x94SiOxe2x80x94) is a cyclic siloxane ring; n is 3 or higher; R is an acyclic alkyl-containing hydrocarbon from C1 to C7; Rxe2x80x2 is H, a vinyl group, or a cyclohexyl group; and m is 1 or greater given that m is chosen such that the resulting molecule remains asymmetric. In some cases, the two groups, R and Rxe2x80x2, are linked together to form a cyclic alkyl group.
Representative asymmetric organocyclosiloxane compounds include but are not limited to 2-vinyl-2,4,4,6,6-pentamethylcyclotrisiloxane (#1), 2-vinyl-4,4,6,6-tetramethylcyclotrisiloxane (#2), 2-vinyl-2,4,6-trimethylcyclotrisiloxane (#3), 2-vinyl-4,6-dimethylcyclotrisiloxane (#4), 2,6-divinyl-4,4-dimethylcyclotrisiloxane (#5), 2,6-divinyl-4-methylcyclotrisiloxane (#6), 2-cyclohexyl-2,4,4,6,6-pentamethylcyclotrisiloxane (#7), 2-cyclohexyl-4,6-dimethylcyclotrisiloxane (#8), 2-cyclopentamethylene-4,4,6,6-tetramethyltrisiloxane (#9), 2-cyclopentamethylene-4,6-dimethyltrisiloxane (#10), 2-cyclotetramethylene-4,4,6,6-tetramethyltrisiloxane (#11), and 2-cyclotetramethylene-4,6-dimethyltrisiloxane (#12), as shown in Figure 1. 
The films that are formed using the above-described substituted organosilane compounds will have dielectric constants, k, of below 2.5, preferably in the range 2.0 to 2.5.
The low-k dielectric films formed by the compounds of the present invention are deposited using pyrolytic or plasma-assisted CVD processes. The siloxane precursor will react or polymerize on the surface of the wafer forming the dielectric layer. The reaction, in part, results in the opening of the cyclic structure and gives better control of organic content and the steric effect of the organic groups in the finished film. Reduction of film density and introduction of nano-pores help to achieve lower k values.
The present invention provides for low-k precursor chemistries and process methods of depositing low-k film using CVD techniques. The process system comprises a precursor delivery manifold system, a vacuum chamber as a plasma CVD reactor, a wafer substrate, and a computer control system.
The low-k precursor of this invention is injected into vacuum chamber with or without a carrier gas. Depending upon the physical properties of a member of the low-k precursor family, either liquid or vapor phase precursor is delivered by a manifold system to the vacuum chamber. The low-k precursor material is placed in a metallic source bubbler. Both pressure and temperature of the bubbler are controlled. For high vapor pressure precursors ( greater than 5 Torr at source temperature from 25xc2x0 C. to 100xc2x0 C.), a direct vapor delivery method based on a pressure mass flow controller can be employed. Typically, the downstream delivery lines as well as a showerhead in the vacuum chamber are heat traced to avoid any condensation. The precursor can also be delivered using a liquid injection method at room temperature. The liquid phase precursor or solution of solid phase precursor can be injected to a vaporizer where it is located at the vacuum chamber. The vaporizer converts liquid phase precursor into vapor phase precursor at the point-of-use. In either case, the precursor is delivered at a rate from 1 sccm to 1000 sccm by the manifold system.
The low-k precursor family of this invention contains the necessary components for making low-k dielectric layers. These components are atoms of silicon, oxygen, carbon, and hydrogen. Therefore, an individual low-k precursor can be used in low-k deposition methods of the present invention. An additional oxygen-containing precursor, such as O2 or N2O, is optional. The additional oxidant and optional inert carrier gases are delivered using thermal mass flow controllers.
The vacuum chamber is a chemical vapor deposition (CVD) reactor. One viable CVD reactor in which the methods of this invention can be practiced is a parallel plate single wafer reactor. The process can be either pyrolytic or plasma-assisted CVD. The total pressure in the reactor is controlled from 0.01 mTorr to 100 Torr. RF power is applied to the upper electrode or the showerhead. The RF power excites the precursor vapors that have been inputted into the vacuum chamber and generates reactive plasma. The frequency of RF is typically in the range of 1 kHz to 3 GHz. A frequency of 13.56 MHz is typical. The RF power can be varied from 1 to 1000 W. The preferred RF power is from 5 to 100 W. The RF power can be pulsed by alternating between on and off. When the duration of RF power on equals zero, the pyrolytic CVD condition is obtained.
A semiconductor substrate, typically a silicon wafer, is placed onto the bottom electrode. The size of the substrate can be up to 300 mm in diameter. The bottom electrode is heated by either electrical resistance heaters or by radiation heaters. The wafer temperature is controlled from 30xc2x0 C. to 500xc2x0 C. The distance from the bottom electrode to the upper electrode can be also varied. Precursors deposited on the hot wafer surface will react and polymerize and this reaction and polymerization is driven by reactive species, thermal and ring strain energies. In this process, the opening and retention of the precursor ring structures of the present invention can be controlled within the low-k films.
A computer system controls the precursor delivery, RF powers, vacuum and pressure in the CVD chamber, as well as the temperature in the delivery manifold and in the reactor.
Low-k films with thickness from 0.5 to 5 microns were characterized for their thermal, mechanical, and electrical properties. The k values were obtained by measuring Aluminum dots MIS capacitance structures at 1 MHz and 0.5-2 Volts.